1. Field of the Invention
The invention relates to a hybrid electric vehicle powertrain, including a multiple-ratio transmission situated between an engine and a motor-generator, wherein engine power and motor-generator power are delivered to the traction wheels through parallel power flow paths.
2. Background Art
A known hybrid electric vehicle powertrain having two-wheel drive characteristics is disclosed in co-pending patent application Ser. No. 10/605,313, filed Sep. 22, 2003, now U.S. Pat. No. 6,994,360, which is owned by the assignee of the present invention. In the powertrain of that co-pending application, power is delivered to the traction wheels from an engine and an electric motor. A generator is electrically coupled to the motor and a battery sub-system acts as an energy storage system for the generator and the motor. Generator speed is varied to control engine speed so that the engine operates at a desired brake specific fuel consumption point on an engine performance curve. Gearing is used to divide the driving power into a mechanical power flow path and an electrical power flow path.
The powertrain disclosed in the '313 patent application requires two electric machines, each of which operates either as a generator or as a motor depending upon the operating conditions.
An all-wheel drive version of the powertrain disclosed in the '313 patent application is disclosed in co-pending patent application Ser. No. 10/747,429, filed Dec. 29, 2003, now U.S. Pat. No. 7,163,480, which also is owned by the assignee of the present invention. In the case of the powertrain disclosed in the '429 application, a traction motor is disposed on a front wheel axis of a vehicle or is drivably connected through gearing to front traction wheels, whereby driving torque is delivered to the vehicle front wheels as engine power and generator power are distributed through a divided power flow path to rear traction wheels. Both of the powertrains disclosed in the co-pending patent applications require two electric machines.